Shares of the diversified miner and energy producer had surged earlier on Thursday after it announced plans to slash its mining capital budget by 25 percent next year and cut 10 percent of its U.S. mine staff.

But the stock climbed further after the billionaire investor disclosed the stake in a filing with the U.S. Securities and Exchange Commission, and said that he plans to speak with Freeport and may seek board representation.

Icahn’s holding is valued at $897 million based on Freeport’s closing stock price of $10.19. The stock rose to $12.18 in extended trade.

Freeport is undervalued, Icahn said in the filing, and he intends to address “executive compensation practices and capital structure as well as curtailment of the issuer’s high-cost production operations.”

In a statement, Freeport said it “welcomes constructive input toward our common goal of enhancing shareholder value.”

Icahn, known for taking on such companies as Apple and Hertz Inc., also disclosed an 8.2 percent stake in Cheniere Energy earlier this month. Just over two weeks later, Cheniere named two of Icahn’s managing directors to the company’s board.

U.S. companies targeted by activists has more than doubled since 2012, with at least 250 campaigns this year, according to Activist Insight, an industry data and media firm. Activists typically push companies to use cash piles to buy back shares, hive off divisions, or be put up for sale to boost shareholder value.

Arizona-based Freeport, which also said it would suspend operations and lower production at some U.S. mines, reduced the 2016 and 2017 oil and gas capital budgets by 31 percent to $2 billion per year on Aug 5.

Freeport now plans to spend $2 billion on mining in 2016, for a total capital budget of $4 billion. Last month it cut total spending to $4.7 billion from $5.6 billion forecast in July.

“This (the cuts) is a step in the right direction to stop the bleeding; however, current copper and oil prices restrict the company’s ability to materially de-lever,” Cowen and Co analyst Anthony Rizzuto wrote in a note to clients.

Freeport acquired two oil and natural gas producers in 2013, bulking up its debt which was $20.9 billion at June 30.

Asset sales may be next if the cuts, a planned $1 billion equity issue and IPO of a minority stake in its energy business are not enough, Jefferies analyst Christopher LaFemina said in a note.

Freeport’s stake in the Cerro Verde copper mine in Peru could fetch $4 billion, the El Abra deposit in Chile $1.1 billion, and the Morenci mining complex in Arizona $1.6 billion, he wrote.

With seven copper mines in North America, Freeport will suspend operations at its Miami mine in Arizona, halve production at Tyrone in New Mexico and “adjust” rates at other U.S. sites, while reducing its workforce by 1,000.

Henderson mine molybdenum production will be cut by 35 percent.

Cash production costs to produce a pound of copper are now estimated at $1.15, down from $1.25 previously.

Seen as a proxy for industrial activity, copper prices sank to six-year lows this week amid ongoing worries over China’s economy.

Freeport lowered its copper sales estimates for 2016 and 2017 by about 150 million pounds. It previously forecast 2016 sales of 5.4 billion pounds. (Additional reporting by Shubhankar Chakravorty in Bengaluru and Michael Flaherty in New York; Editing by Savio D’Souza, Marguerita Choy and Bernard Orr)